1. Field of the Invention
The present invention relates to nozzle assemblies for fluid atomization, and particularly to nozzle assemblies useful in fuel burning apparatus to accomplish the atomization of the fuel in an auxiliary fluid such as air or steam.
2. Description of the Prior Art
Liquid fuel burning devices operating by the combustion of atomized liquid fuel are well known. In particular, a variety of such devices have long been in use in connection with oil burners, as it is equally well recognized that efficient fuel combustion is achieved when the liquid fuel is disposed in an extremely finely divided state of minute droplets, to maximize flame contact. Generally, fuel atomization is conducted under elevated pressures, with the pressure of the atomizing medium, be it air or steam, maintained at a constant differential pressure residing above the fuel pressure, while the pressure of the fuel is varied depending upon the operational requirements of the burner system.
In the past, burner nozzles have utilized a variety of means for effecting atomization, ranging from single to multiple mixing nozzles wherein the respective conduits of the fuel and auxiliary fluid are brought together at a variety of angles with respect to each other, to achieve atomization. For example, U.S. Pat. No. 777,680 to Lassoe et al. discloses an oil burner with coaxially disposed conduits, an oil tube disposed within a steam tube. The oil tube terminates in a reduced section that opens into a chamber into which feed a multiplicity of reduced diameter conduits carrying the steam from the steam tube. Thus, oil and steam intermix and atomization takes place, and the resulting atomized mixture is discharged into the combustion chamber.
A variety of differing nozzle elements are shown and disclosed in the following U.S. Patents: U.S. Pat. No. 4,002,297 to Pillard; U.S. Pat. No. 3,739,990 to Triggs; U.S. Pat. No. 3,362,647 to Davis, Sr. et al.; U.S. Pat. No. 3,130,914 to Carkin et al.; and U.S. Pat. No. 3,072,334 to McKenzie. All of the foregoing patents employ a nozzle element that provides for mixture and atomization of the fuel and auxiliary fluid, to take place at the junction of the respective conduits, in which the respective conduits are either concurrent in their flow or, at most, flow transversely toward each other.
In similar fashion, U.S. Pat. No. 4,195,780 to Inglis discloses a nozzle construction for the metered flow of a fluid under pressure, wherein the fluid is introduced into an outer fluid flow in essentially concurrent relationship thereto.
U.S. Pat. No. 1,669,810 to Clapham discloses an oil burner gun having a deflector at the end of a fuel inlet pipe, that has a cup-shaped recess, that appears to direct incoming fuel radially outward into an oncoming stream of air. The direct deflection of the Clapham device, however, has its drawbacks, as streams of fuel may, for example, emerge that are insufficiently atomized, and are inadequately burned. Also, nonuniform fuel atomization can cause high velocity streaks of burning fuel that can damage furnace linings by causing impingement.
One of the difficulties that attends the efficient operation of fuel burning devices, and particularly oil burners, relates to the increased velocities at which such atomization burning devices must operate. Particularly at the present time, wherein fuels of lower grade, with higher residual nonvolatile components, presents problems of combustion efficiency, fuel cost and air pollution. In particular, the heavier fuels containing these nonvolatile components, are more difficult to burn, and the unburned fractions tend to coat the burners and form carbon deposits that can clog the burners and further reduce their operating efficiency. Likewise, the release of unburned fuel fractions into the air, causes an air pollution problem requiring substantial expenditures of time and resources to abate. It has therefore been determined that the only way in which such fuels may be efficiently burned, is to achieve maximum atomization at increased fluid pressures, to effect the maximum dispersion of the fuel droplets. This approach, however, has its drawbacks in that burner operation frequently varies from maximum to lower capacities, and with the use of increased fluid pressures, more fuel may be burned and therefore, used, than is necessary to achieve fuel efficiency while minimizing the adverse effects mentioned above.
Desirably, fuel atomization should be achieved at lower emission velocities, to maximize combustion and to reduce residual unburned fuel so as to maximize the heat utilization and recovery. At present, however, attempts to achieve efficient fuel atomization at lower pressures and emission velocities, have been unsuccessful, with the adverse results mentioned earlier herein.
Accordingly, it is desirable to achieve maximum fuel atomization at lower emission velocities, to provide a means for efficient fuel consumption in the instance of reduced burner operational requirements.